Many types of optical recording media use a sinusoidal wobble signal for synchronizing the write pulses during recording. This wobble signal also contains address information for position and address recordings. U.S. Pat. No. 6,765,861 mentions a wobble using a single phase modulation, where a logic “1” is represented by four inverted sines (18° phase shifted sines), a logic “0” is represented by four non-inverted sines (0° phase). A similar modulation scheme is used for example in the SYNC unit of the DVD+RW, where four inverted wobbles are provided for word sync followed by four non-inverted wobbles. See ECMA-337: Data Interchange on 120 mm and 80 mm Optical Disk using +RW Format—Capacity: 4,7 and 1,46 Gbytes per Side. For this medium most wobble periods are non-inverted, only a small number of wobble periods are inverted. In other words, the phase encountered for the majority of wobble periods defines which wobble periods are to be considered as inverted.
To detect a wobble address the phase of the wobble signal has to be detected. This detection is usually accomplished by multiplying the filtered analog wobble signal with a reference signal (sine) from a locked wobble PLL and integrating the result over one wobble period. The integration result is positive for a wobble signal without phase shift and negative for a phase shifted signal. However, under certain circumstances, e.g. in case of noise or a low signal amplitude, a misdetection of the signal phase can occur. This in turn may lead to a misdetection of the address information. To improve the reliability of the wobble detection, it is known from e.g. U.S. Pat. No. 6,765,861 to integrate the analog wobble signal multiplied with the reference signal over more then one wobble period. In this case, however, a state machine has to be locked to the data stream.